The present invention relates generally to thermal control devices, more particularly to a device, system and methods for thermal cycling in a nucleic acid analysis.
Various biological testing procedures require thermal cycling to facilitate a chemical reaction via heat exchange. One example of such a procedure is polymerase chain reaction (PCR) for DNA amplification. Further examples include, rapid-PCR, ligase chain reaction (LCR), self-sustained sequence replication, enzyme kinetic studies, homogeneous ligand binding assays, and complex biochemical mechanistic studies that require complex temperature changes.
Such procedures require a system that can accurately raise and lower sample temperatures rapidly and with precision. Conventional systems typically use cooling devices (e.g., fans) that occupy a large amount physical space and require significant power to provide a required amount of performance (i.e., a rapid temperature drop). Fan based cooling systems have issues with start-up lag time and shutdown overlap, that is, they will function after being shut off and thus do not operate with rapid digital-like precision. For example, a centrifugal fan will not instantly blow at full volumetric capability when turned on and will also continue to rotate just after power is shut off, thus implementing overlap time that must be accounted for in testing. Such lag and overlap issues frequently become worse with device age.
The fan based cooling systems have typically provided for systems with low cost, relatively acceptable performance and easy implementation, thus providing the industry with little incentive to resolve these issues. The answer thus far has been to incorporate more powerful fans having greater volumetric output rates, which also increase space and power requirements. One price of this is a negative effect on portability of field testing systems, which can be used, for example, to rapidly detect viral/bacterial outbreaks in outlying areas. Another problem is that this approach is less successful in higher temperature environments, such as may be found in tropical regions. Accordingly, there is an unanswered need to address the deficiencies of known heating/cooling devices used in biological testing systems.
Thermal cycling is typically a fundamental aspect of most nucleic acid amplification processes, where the temperature of the fluid sample is cycled between a lower annealing temperature (e.g. 60 degrees) and a higher denaturation temperature (e.g. 95 degrees) as many as fifty times. This thermal cycling is typically carried out using a large thermal mass (e.g. an aluminum block) to heat the fluid sample and fans to cool the fluid sample. Because of the large thermal mass of the aluminum block, heating and cooling rates are limited to about 1° C./sec, so that a fifty-cycle PCR process may require two or more hours to complete. In tropical climates, where ambient temperatures can be elevated the cooling rates can be adversely effected thus extending the time for thermal cycling from, for example, 2 hours to 6 hours.
Some commercial instruments provide heating rates on the order of 5° C./second, with cooling rates being significantly less. With these relatively slow heating and cooling rates, it has been observed that some processes, such as PCR, may become inefficient and ineffective. For example, reactions may occur at the intermediate temperatures, creating unwanted and interfering DNA products, such as “primer-dimers” or anomalous amplicons, as well as consuming reagents necessary for the intended PCR reaction. Other processes, such as ligand binding, or other biochemical reactions, when performed in non-uniform temperature environments, similarly suffer from side reactions and products that are potentially deleterious to the analytical method.
For some applications of PCR and other chemical detection methodologies, the sample fluid volume being tested can have a significant impact on the thermal cycling.
Optimization of the nucleic acid amplification process and similar biochemical reaction processes typically require rapid heating and cooling rates such that the desired optimal reaction temperatures can be reached as quickly as possible. This can be particularly challenging when performing thermal cycling in high-temperature environments such as found in tropical climates where facilities may often lack climate control. Such conditions may result in longer thermal cycling times with less specific results (i.e. more undesired side reactions). Therefore, there is an unmet need for thermal control devices with greater heating and cooling rates that are not dependent on the ambient environment and can be produced at low cost and minimal size for inclusion in diagnostic devices. There is further need for thermal control devices that better control temperature cycling within a reaction chamber within the required scope of speed, accuracy, and precision of current generation systems.